This invention relates to a continuous process for production of hydrogen peroxide from hydrogen and oxygen gases.
Such process which has been used commercially involves two stages of operation, one being an oxidation stage in which a 2-alkyl-9,10-dihydroxyanthracene is contacted with oxygen gas in an organic solvent whereby the alkyldihydroxyanthracene is oxidized to the corresponding alkylanthraquinone and to hydrogen peroxide coproduct which is recovered by extraction with water; and a reduction stage in which the said alkylanthraquinone is catalytically reduced by hydrogen back to the alkyldihydroxyanthracene starting material.
Among disadvantages of this process are the fact that the hydrogenation catalysts employed (specifically palladium on alumina) tend to produce hydrogenation of the anthraquinone ring as well as the desired hydrogenation back to the dihydroxyanthracene compound; that the hydrogenation catalyst, to the extent carried over into the oxidation stage, acts to decompose hydrogen peroxide product; and that the water, used to extract out the hydrogen peroxide products, tends to form emulsions with the organic solvent.
It has been disclosed in the literature that complexes of rhodium with bidentate nitrogen-containing chelating ligands are useful hydrogenation catalysts both for ketones, including aromatic ketones such as acetophenone, and for olefinic bonds. (J. Organomet. Chem. vol. 140 of 1977, pp. 63-72; ibid. vol. 157 of 1978, pp. 345-352). In hydrogenation of alkylanthraquinones to the dihydroxyanthracenes it is important that the hydrogenation be highly selective for the ketone group vs. the anthraquinone rings. The above literature indicates that high selectivity may be observed for ketone or for olefinic bond hydrogenation, depending on the substrate to be hydrogenated and on the complex used.
It has been proposed to carry out redox processes across membranes by use of quinone-type carriers (Nature, Vol. 265 of 1977, pages 229-230). Such processes, specifically, used a diphenyl ether membrane supported on a filter of cellulose nitrate and containing a suitable carrier molecule, specifically 2-methyl-1,4-naphthoquinone. An aqueous solution of sodium dithionite or ascorbic acid reducing agent was separated from an aqueous solution of potassium ferricyanide by the diphenyl ether membrane containing the carrier molecule. Occurrence of electron transfer through the membrane was demonstrated by observation of the reduction of the ferricyanide to the ferrocyanide form, when the quinone carrier molecule was included in the membrane.